The removal of sulfur compounds from various hydrocarbon streams and especially gasoline and diesel streams is becoming more critical with the introduction of legislation limiting the amount of sulfur in such streams. The most common way of removing the bulk of the sulfur present in various hydrocarbon streams is hydrodesulfurization (HDS) which involves contacting the stream with a hydrodesulfurization catalyst in the presence of hydrogen at elevated temperatures and pressure. HDS is part of an overall process commonly referred to as hydrotreating. Hydrotreating includes HDS, hydrodenitrogenation (HDN) and hydrogenation (HYD). Hydrogenation (HYD) can be an undesirable reaction during hydrotreating.
Catalysts which are commonly used for hydrotreating and HDS in particular include those with molybdenum or tungsten as the active species in combination with other transition metal compounds such as nickel or cobalt. Usually these catalysts are dispersed on some type of support in order to maximize the effectiveness of the metals. Additionally, other additives such as phosphorus can be incorporated into the support either to stabilize the surface area of the support or to prevent formation of compounds such as cobalt or nickel aluminate.
WO 01-23501 A1 discloses the use of transition metal phosphide catalysts for hydrodesulfurization processes. The catalyst is described as a metal phosphide complex having the formula MP, where M is selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Ta and W, and “x” ranges from 0.1 to about 10. This metal phosphide catalyst is supported on a high surface area support. The catalyst can also be a mixed metal phosphide having the formula AaBbPy where A and B are each selected from the group described above, the sum of a and b is 1, the ratio of a:b is between 0.01 and 100 and y is between 0.1 and 10.
In contrast to this, applicants have developed a catalyst comprising a metal phosphide and a promoter metal component and where at least a portion of the promoter metal component is present on the metal phosphide and the metal phosphide/promoter metal components are dispersed on a refractory inorganic oxide support. The catalyst is capable of removing sulfur and nitrogen compounds from various hydrocarbon streams with less hydrogenation of unsaturated or aromatic components.